This invention relates to chucks for machine tools and more particularly to chucks of the cam operated type. In this type of chuck, the work clamping jaws are secured to supports which are movably mounted on a chuck body. The supports are shifted between work clamping and work release positions by levers which in turn are controlled by an actuator. The actuator normally is shifted lengthwise of the chuck by suitable means such as a push rod which may be hydraulically, pneumatically or mechanically operated.
A significant problem with this type of chuck has been assurance that it will, without fail, maintain its clamping grip on the work piece. This is a serious safety matter because unintentional release of the work piece can cause serious injury to personnel as well as damage or destruction of the work piece itself. This problem is complicated by the fact that chucks operate rotationally and the higher the r.p.m. the greater the centrifugal forces tending to open the jaws of the chuck. As costs increase, the demand for higher chuck speeds to reduce production time also increases. This further complicates the problem.
To deal with this problem it is standard practice to maintain the actuator under a continuous positive force to assure its remaining in the proper position to maintain the jaws in clamped position. However, occasionally this restraining force fails and inadvertent work piece release occurs.